This will grow until effective measures are taken. Looking back at the PLO bombing campaign in Israel, the PLO started slow with 4 or five attacks a year then accelerated to more than 40 a year. What ever Europe needs to do, they need to do it now before it gets to be an every day occurrence or WMD are used.
https://en.wikipedia.org/wiki/List_of_Palestinian_suicide_attacks#1990s